1. Field of the Invention
The present invention relates to an image projection apparatus configured to control at least one of a light source unit and a light modulation unit.
2. Description of the Related Art
An image projection apparatus such as a projector is capable of projecting any image by modulating light from a light source unit at a light modulation unit and projecting the modulated light on a projection surface. The image projection apparatus includes, for example, a lamp or an LED as the light source unit and a liquid crystal panel as the light modulation unit.
In such an image projection apparatus, aging of the light source unit and the light modulation unit changes the brightness of the image projected on the projection surface. The aging of the light source unit changes its output and hence the luminance of the projected image. Furthermore, the aging of the light modulation unit changes the modulation efficiency of the light and hence the luminance and chromaticity of the projected image. This prevents the projected image from being projected at desired brightness in some cases.
Japanese Patent Laid-open No. 2009-199098 discloses a projector that controls one of a light source and a spatial light modulation device based on a relation between the temperature and luminance distribution of the light source and thereby reduces uneven color. Japanese Patent Laid-open No. 2009-199098 discloses a configuration in which a plurality of light sensors are arranged in a matrix and the spatial light modulation device is controlled based on the luminance distributions of RGB lights to make the luminance distributions identical, thereby keeping the brightness even and reducing uneven color. Japanese Patent Laid-open No. 2011-223350 discloses a projector that adjusts a drive signal of each panel based on a test image of even chromaticity by using illuminance/chromaticity sensors distributed on a light shielding shutter, thereby reducing change due to aging in the brightness of an image projected on a projection surface.
However, the configuration disclosed in Japanese Patent Laid-open No. 2009-199098 cannot, when a correlation between values measured at the sensors and the brightness of the projected image changes, keep even the brightness with high accuracy and cannot reduce uneven color. To correct the brightness and uneven color based on the luminance distributions measured at the light sensors, the light sensors need to be arranged in a matrix, which increases cost for the sensors.
In the configuration disclosed in Japanese Patent Laid-open No. 2011-223350, the light shielding shutter needs to be closed to measure the illuminance/chromaticity of the projected image with the illuminance/chromaticity sensors. The illuminance/chromaticity thus cannot be measured while the image is being projected. Furthermore, the light shielding shutter needs a plurality of illuminance/chromaticity sensors, which increases cost for the sensors.